This invention relates to electro-mechanical connectors that make pressed electrical connections between matching sets of signal pads on two separate modules. More particularly, this invention relates to the structure of the above type of connectors where the pressed electrical connections that are made are co-axial connections.
In many types of digital electronic systems, pressed electrical connections are made between a set of multiple signal pads on one module and a matching set of signal pads on another module. One prior art structure for making pressed electrical connections is shown, for example, in U.S. Pat. No. 5,967,798 which is entitled "Integrated Circuit Module Having Springy Contacts Of At Least Two Different Types For Reduced Stress". Pressed Connections are used, instead of soldered connections, where the connections between the two modules need to be made and broken multiple times.
However, in the above-referenced patent, the pressed electrical connections which are made are not co-axial connections. With a pressed co-axial connection, one signal pad is connected to another signal pad by a springy signal contact which is surrounded by a ground conductor that is spaced-apart from the springy signal contact. In the above-referenced patent, the springy signal contact is not surrounded by any ground conductor or any other conductor.
When a springy signal contact is not surrounded by a ground conductor, the characteristic impedance of the contact will vary and is difficult to set to a particular desired value, such as fifty ohms. Consequently, reflections will occur in the electrical signals that are sent from one module thru the springy signal contact to the other module.
But, when the springy signal contact is surrounded by a ground conductor, the characteristic impedance of the contact is fixed and can be accurately set to a predetermined value Zo, where Zo equals 138/(.EPSILON.r).sup.1/2 log(D/d). Here, "d" is the diameter of the springy signal contact; "D" is the inside diameter of the ground conductor which surrounds the springy signal contact; and .EPSILON.r is the relative permitivity of a dielectric which fills the space between the ground conductor and the springy signal contact.
One way to fabricate a connector which makes multiple pressed co-axial connections is to start with a conductive block that has a plurality of holes of diameter D. Next, the holes are completely filled with a solid dielectric which has a relative permitivity .EPSILON.r, such as a plastic. Then, in the center of each dielectric filled hole, a smaller hole of diameter d; is drilled. Lastly, a springy signal contact is press-fit into each hole of diameter d; and a ground terminal is attached to the conductive block.
However, with the above connector, a decrease in yield occurs as the diameter D decreases. This is because as D decreases, the step of drilling the holes of diameter d becomes more difficult. Further, with the above connector, the maximum number of signal conductors per unit area is limited by the permitivity .EPSILON.r of the solid dielectric. This is because for any given Zo and d, the diameter D increases as .EPSILON.r increases. Also, with the above connector, costs are incurred by the steps of filling the holes of diameter D with the solid dielectric and subsequently drilling the smaller holes in that dielectric.
Accordingly, a primary object of the present invention is to provide a connector for making multiple pressed co-axial connections in which the above problems are avoided.